1. Field of the Invention
The present invention relates to an exposure control device, and more particularly, to such an device which is particularly suitable for use in high-speed, precision applications.
2. State of the Prior Art
Magnetic actuators are known for moving elements in various types of mechanisms. In certain of these mechanisms, it is desirable for the movable element to be as light as possible, to move silently, and with a minimum of friction. One of the problems in magnetic actuators of a bidirectional type is that a magnetic element, such as a coil or a permanent magnet, must be incorporated in the movable element; this increases the mass of the element and hence the power requirements of the actuator.
In U.S. Pat. No. 4,051,499, there is disclosed a focal plane shutter having leading and trailing blinds made of opaque plastic sheet material. A thin permanent magnet is sealed in each of the blinds. A series of electromagnetic coils are located along the path of each blind, and the coils are sequentially energized to drive the blinds in accordance with the principle of a linear motor. Such an arrangement has the disadvantage that a number of coils and relatively complex drive electronics are required. It also has the disadvantage noted above, that is, the movable elements have a relatively high mass as a result of the magnets being incorporated in the blinds.